340 heads on 360?

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Elís Máni

Elís Máni

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So i have a 1973 Duster that was originaly a 340 4-speed. unfortunately at some point in its life the engine froze and it cracked the 340 block. now it has a 360 out of a 1980's Ram with the 73 heads on it. i'm just wondering if and what 340 heads change on the 360. does it increase compression?, does it have bigger intake valves? or something, just general questions.
im kinda new too this so yeah.

Thank you,
-Elís M
 
Other than the 2.02" intake valve on the 68-71 340's heads they are all basically the same accept for the T/A head (good luck finding a pair and buck up if you do) and the 308 casting head, as it is reported to flow better (someone correct me if I'm wrong).
 
Like said above only difference is 2.02 intake valves. You can have those valves installed in you heads if you get the seats machined. Don't know what kind of services you have available in Iceland.
 
HemiSSDart said:
Like said above only difference is 2.02 intake valves. You can have those valves installed in you heads if you get the seats machined. Don't know what kind of services you have available in Iceland.
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There is probably someone who does that here in iceland but it would most likely be pretty expensive. thank you.
 
Elís Máni said:
There is probably someone who does that here in iceland but it would most likely be pretty expensive. thank you.
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Agreed. You'll have over a grand in the heads. YOu might as well just buy a set of aluminum heads with 2.02 valves at that point.
 
a 73 340 is going to have the same intake valve size as the later 360 head, 1.88.

73 shouldn't have a 2.02
 
"X", "J", or "915" heads normally have open chambers, so I would expect a slightly lower compression ratio when they are put on a 360. All else being equal.
 
Most of the later 340 heads & 360 heads had the 1.88 intake valves. Unless you are running a much bigger than stock cam or running extreme RPM's, the 2.02 valves won't get you much more. JMO
 
Until the heads changed to magnums, they were all open chamber, IIRC. Even 308's were open.
 
I used to have a small stack of X J U and Os, These were all very early examples and I think all were 2.02s..Without measuring them, and not actually having seen them now for over 12 years, they did look the same on the chamber side. I started selling them to stock-class racers.
I have another small stack of big-port,small-valve heads, IIRC all are Js,

For a streeter, I sure wouldn't spend money to up the valve sizes. And Why? Well if you run 3.55 street type gears, and an automatic, you won't hit 5000 until about 45 mph and she'll be spinning all the way,lol, anyway.and in about 1 second you'll be outta revs. Then you won't see 5000 again until around 75mph.
 
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crackedback said:
Until the heads changed to magnums, they were all open chamber, IIRC. Even 308's were open.
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Nooooo, the late '80's-early '90's heads were fast-burn Heart-shaped chambers with a definite squish zone, which is why they could run stock small rollers w/ 9:1 comp.
on regular 87 octane................
 
Elís Máni said:
There is probably someone who does that here in iceland but it would most likely be pretty expensive. thank you.
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As stated, they are the same head, even the valve size for that year. It is not worth anything to buy TA heads even if You could find them, they are "J" heads that simply
had the pushrod holes drilled offset out to enable wider porting at the "pinch", which won't give You squat if You don't do a lot of port development elsewhere first.
I disagree completely that it wouldn't help much to install 2.02's with a proper bowl-cut blend & valve-job, but You really would have to weigh actual costs there, ??????
The upshot is, nothing lost & nothing gained with Your combo other than You picked up 20 cubes, ...& whatever actual difference in compression was & is between the 2..
 
Killer6 said:
Nooooo, the late '80's-early '90's heads were fast-burn Heart-shaped chambers with a definite squish zone, which is why they could run stock small rollers w/ 9:1 comp.
on regular 87 octane................
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YESSSSSSSS...

302 heads, yes

308 heads no

The 88-89 360 roller motor I took apart had 308 heads on it. IIRC

Exactly like these that prine posted years ago. Shaft rockers/LA oiling on a roller 360 block.
how to port swirl ports

Here's another deal talking about the 88-92 308 head.
How to Build Mopar Engines for Performance: Cylinder Heads - Mopar DiY
 
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Lol! Yesss.. 302's are not 360 port heads, but they are SB heads,.......not that I haven't considered trying a full-on ported set of 302's on a street 360 for chicks & jiggles...
 
The 308 was introduced in 1988 and had large diameter pushrod hole.To compensate the intake roof was raised to get more area and offers more hp potential.The exhaust port also has a W2 short side radius and improved shape.
I have no first hand experience with these heads but they are suppose to be the best according to Larry Sheppard
 
sorry for the double post CrackedBack..i only just now read your attachments.
Also i rarely post anything i have no hands on experience with..especially magazine or TV articles that have endorsement potential..but Larry Sheppard has some pretty good credentials.
 
Killer6 said:
Lol! Yesss.. 302's are not 360 port heads, but they are SB heads,.......not that I haven't considered trying a full-on ported set of 302's on a street 360 for chicks & jiggles...
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The post is about 340 and 360 heads, not those 302 door stops
 
replicaracer43 said:
The post is about 340 and 360 heads, not those 302 door stops
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And his comment about chambers is only about the 318 head until 92, but, I'm still wrong. I enjoy when people hit the disagree tab and are dead wrong. :)

360 heads were open chamber until 92. They did call those 308 heads swirl port, but didn't close the chamber.
 
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  • 308 is open chamber, found on 360's later '80's up to '92. They used 1.88/1.60 valves. Exhaust side flows well, but the heads are prone to cracking between the seats. I've used a set, still have them, and they are cracked.
  • 302 is a "closed" chamber 318 head used in late 80's-91. 1.78/1.50 valves Also known for cracking.
  • J heads really have no advantage over 360 heads, and even the smog heads will perform just fine, and port like no tomorrow. :D
 
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318willrun said:
  • 308 is open chamber, found on 360's later '80's up to '92. They used 1.88/1.60 valves. Exhaust side flows well, but the heads are prone to cracking between the seats. I've used a set, still have them, and they are cracked.
  • 302 is a "closed" chamber 318 head used in late 80's-91. 1.78/1.50 valves Also known for cracking.
  • J heads really have no advantage over 360 heads, and even the smog heads will perform just fine, and port like no tomorrow. :D
Click to expand...
Are there other quench-type heads ,post 1975 say?
 
318willrun said:
  • 308 is open chamber, found on 360's later '80's up to '92. They used 1.88/1.60 valves. Exhaust side flows well, but the heads are prone to cracking between the seats. I've used a set, still have them, and they are cracked.
  • 302 is a "closed" chamber 318 head used in late 80's-91. 1.78/1.50 valves Also known for cracking.
  • J heads really have no advantage over 360 heads, and even the smog heads will perform just fine, and port like no tomorrow. :D
Click to expand...

The 308 360 head has a REALLY good exhaust port in it. Too bad they crack like crazy. Out of 8 308 heads I've had, 1 was OK. The other 7 were cracked.
 
I have a set of 308s on my asphalt circle track engine, un ported but excellent valve job, 11/32 valves ect... they worked quite well....see avatar for example
 
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